Hill slope stability analysis using two and three dimensions analysis: A comparative study

Slope instability is very common phenomenon, especially in tectonically active hills of the lesser Himalaya. The deformed, weathered and fragile rocks of the lesser Himalaya are often vulnerable under natural or anthropogenic influences. There were several cases of slope failure along highway sections in Uttarakhand Himalaya. The study was carried out along a highway section of NH-109. The factor of safety (FoS) is commonly most acceptable parameter that analyses the health of slopes. The two dimensional (2D) numerical analysis techniques are commonly used to obtain the FoS. It is observed that many times FoS obtained from 2D analysis techniques do not qualify the actual conditions and are usually lower in value as compared to ground conditions. This, in turn, increases the cost of remedial measures used for protection of slopes. This paper presents a comparative study of 2D and 3D numerical analysis based on the finite difference method (FDM) using fast Langrangian analysis of continua (FLAC) codes. The study indicates that there is no appreciable difference between FoS values obtained from 2D and 3D analysis based on the selected slope conditions. The difference ranges from 0.02 to 0.07 for analysed cases in uniform rock mass. The study also exhibits some of the important analytical observations and effects of variables on resultant FoS.